[lug] OT: UDP multicast question

[Scott A. Herod]

In his _Network Programming, Vol. 2_ , Stevens has an example of
a one-to-many fifo based broadcaster.  That's what I'll probably
use.  However, all I really want to do is send a note to many
processes that table T, row R changed so that if they care they
should go look to see what happened.  I want to make the message
route as simple as possible and avoid polling ( other than internal
select() calls ).

Scott

"D. Stimits" wrote:
> 
> "Scott A. Herod" wrote:
> >
> > Hello,
> >
> >   I'm not much of a network programmer so this may be an
> > obvious question.  Can I have multiple processes on a single
> > machine listening to a local udp multicast?  This is with IPv4,
> > but would IPv6 make a difference?  (MySQL doesn't implement
> > triggers and I need to tell several processes when a table
> > changes.)
> 
> I wouldn't try it with IPv4, don't know if IPv6 is different. As soon as
> a process reads the buffer you can expect the data to go away, or else
> for it to be marked as empty. I'd guess the same is true for IPv6 but
> don't know. You would probably be better off creating a surrogate daemon
> that does the listening, has either an update buffer or a notification
> of change, and allows multiple subscribers; it would publish to anything
> subscribed. You could go as far as to offer an ability to subscribe to
> particular sql servers, databases within servers, tables within
> databases, so on. Then you are totally isolated from the type of sql
> server. Lots of fun things you can do with it, depending on what you
> want as the end goal, but I doubt you'll get anything other than
> surprises if you have multiple processes trying to listen to the same
> UDP socket and expecting them to get the same information.
> 
> D. Stimits, stimits at idcomm.com